ASCP MLS MOLECULAR DIAGNOSTICS EXAM QUESTIONS AND ANSWERS 100% VERIFIED
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ASCP MLS MOLECULAR DIAGNOSTICS
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ASCP MLS MOLECULAR DIAGNOSTICS
ASCP MLS MOLECULAR DIAGNOSTICS EXAM QUESTIONS AND ANSWERS 100% VERIFIEDASCP MLS MOLECULAR DIAGNOSTICS EXAM QUESTIONS AND ANSWERS 100% VERIFIEDASCP MLS MOLECULAR DIAGNOSTICS EXAM QUESTIONS AND ANSWERS 100% VERIFIED
Which double-stranded DNA molecule has the highest melting temperature?
A. An oli...
ASCP MLS MOLECULAR DIAGNOSTICS
EXAM QUESTIONS AND ANSWERS
100% VERIFIED
Which double-stranded DNA molecule has the highest melting temperature?
A. An oligonucleotide with a repeating sequence of A-A-A at the 5´ end
B. A molecule of 5,000 base pairs with a high number of A-T base pairs
C. An oligonucleotide with a large number of repeating C-G-C codons
D. A DNA polymer of 100,000 base pairs - ANSWER-C. The melting temperature of
DNA refers to the
temperature required to separate the molecule into
single strands. The Tm is the temperature required to
convert half of the DNA from dsDNA to ssDNA. This is
done by breaking the hydrogen bonds between base
pairs. A-T base pairs have two hydrogen bonds, while
C-G base pairs have three. Therefore, molecules with
a high proportion of C-G base pairs are more resistant
to heat denaturation or melting.
Which base pair sequence is most likely to serve as a binding site for a restriction
endonuclease?
A. A-T-T-C-A
T-A-A-G-T
B. C-T-A-C-T-G
G-A-T-G-A-C
C. C-A-C
G-T-G
D. A-A-G-C-T-T
T-T-C-G-A-A - ANSWER-D. Restriction endonucleases are enzymes that cut double-
stranded DNA into fragments and are important tools used in molecular diagnostics.
Each restriction enzyme recognizes a specific oligonucleotide sequence, and the size
and number of fragments it produces when DNA is digested depend upon the number
of times that sequence is repeated in the DNA molecule. Restriction endonucleases
,recognize palindromic sequences (i.e., the base sequence of complementary strands
reads the same from opposite directions). The sequence
A-A-G-C-T-T
T-T-C-G-A-A
is the recognition site for HindIII, a restriction endonuclease isolated from Haemophilus
influenzae. If a disease gene produces a base pair substitution at the restriction site, the
enzyme will not recognize it and not cut the DNA. This results in a longer fragment that
can be recognized by electrophoresis. This process was initially used to identify the
hemoglobin S gene using the restriction enzyme MstII. The point mutation changes an
A to a T within the restriction site, causing loss of the normal-sized fragment.
Cloning a human gene into a bacterium in order to make a large molecular probe
requires which vector?
A. Plasmid
B. Bacterial microsome
C. 30S bacterial ribosome
D. Single-stranded DNA - ANSWER-A. A plasmid is a piece of circular double-stranded
DNA
located in the cytoplasm of a bacterium. Although
not attached to a chromosome, the plasmid is
replicated like chromosomal DNA. The plasmid is cut
with the restriction endonuclease that is used to
isolate the DNA fragment containing the gene of
interest. The fragment anneals to the sticky ends of
the plasmid DNA, and the cut is repaired by DNA
ligase. The recombinant plasmid is added to a culture
of bacteria that is disrupted to promote the uptake of
plasmid DNA. Commercially available plasmids have
promoter and reporter genes such as lac and lacZ
that produce β-galactosidase. These can be used to
identify colonies with successful recombinants. They
also carry antibiotic resistance genes that allow the
recombinants to be purified. Culture of the
recombinant bacteria results in large amounts of the
gene, which can be harvested using the restriction
enzyme, denatured, and labeled to make the probe.
What process can be used to make a DNA probe produce a fluorescent or
chemiluminescent signal?
A. Enzymatic attachment of acridinium esters to terminal ends of the probe
B. Substitution of biotinylated or fluorescent nucleotides into the probe
C. Splicing the gene for β-galactosidase into the probe
,D. Heat denaturation of the probe followed by acid treatment - ANSWER-B. Fluorescent
or enzyme labels can be attached to probes by nick translation. A DNase is used to cut
the probe at a few phosphodiester linkages. PolI repairs the nicks by removing
nucleotides from the 3´ end and replacing them with labeled nucleotides at the 5´ end of
the nick. Alternatively, a primer containing a labeled nucleotide can be used to make
copies of the probe by DNA amplification (PCR). A common label used for probes
consists of biotin conjugated to the 5' end of the probe. After hybridization, streptavidin
conjugated to an enzyme such as alkaline phosphatase is added.
Streptavidin strongly binds to biotin, forming an enzyme-labeled complex with the DNA.
After washing
to remove unbound streptavidin, a colorimetric, fluorescent, or chemiluminescent
substrate is added.
Which of the following types of mutation causes the premature termination of protein
synthesis?
A. Missense
B. Nonsense
C. Insertion
D. Frame shift - ANSWER-B. A nonsense mutation occurs when a nucleotide
substitution within a codon changes the code from
that for an amino acid to a stop sequence. For
example, a change from TTC to GTC changes the
mRNA transcript from AAG to UAG. AAG codes for
lysine and UAG is a stop codon; therefore, instead of
lysine being added to the protein during translation,
protein synthesis is terminated. In the reverse
situation, the point mutation changes a termination
codon into one for an amino acid and a longer
protein is produced. A missense mutation occurs
when a base substitution alters the codon so that a
different amino acid is inserted during translation. A
frame shift mutation occurs when there is a deletion
or insertion of more or less than three bases. This
changes the triplet order, altering the amino acid
sequence of the protein.
In humans, which component of a gene is translated into a protein?
A. Intron
B. Exon
C. Promoter
D. TATA box - ANSWER-B. Exons are the components of genes that determine
the amino acid sequence of the protein synthesized.
Exons are separated by noncoding regions called
, introns that are transcribed and later removed from
mRNA before translation. Promoters are sequences
located near the gene at the 5´ end and facilitate
binding of proteins that increase transcription. A
TATA box is an oligonucleotide sequence often found
in the promoter region. The AT base pairs have two
hydrogen bonds that separate more easily than CG
bonds, thus creating a point where the double helix is
easier to open.
What term describes the products produced when DNA is digested by restriction
endonucleases?
A. Mosaicisms
B. Chimeras
C. Amplicons
D. Restriction fragment length polymorphisms - ANSWER-D. Mosaicism occurs when
cells within the same
individual contain different numbers of chromosomes
and results from nondisjunction during early
embryonic development. Chimeras are molecules
created when translocation occurs between genes
(exons) on different chromosomes. Amplicons are
exact copies of a DNA template produced by DNA
amplification techniques such as the polymerase
chain reaction (PCR). When a restriction enzyme cuts
two different DNA molecules, the size of some
fragments will differ because the number and position
of restriction sites differ. Such fragments are called
RFLPs for restriction fragment length polymorphisms
(RFLPs). Analysis of RFLPs can be used to test for
disease genes, study genetic linkage, and establish
identity. It is used usually when PCR is impractical,
such as when contamination occurs repeatedly or
when the genes to be analyzed comprise a length of
DNA too long for efficient amplification.
What reagent is most commonly used to stain DNA separated by electrophoresis?
A. Silver nitrate
B. Nicotinamide adenine dinucleotide
C. Cationic dye
D. Ethidium bromide - ANSWER-D. When ethidium bromide inserts between the base
pairs of double-stranded DNA, the dye becomes
fluorescent, releasing 480 nm light when stimulated by
long wavelength ultraviolet light. Ethidium bromide
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